Touchscreen panels are typically incorporated in various electronic devices to detect a user input (i.e., user touch or hover) and to display content. The touchscreen panels include an active portion capable of detecting the user touch/hover and displaying content. This active portion is typically formed from a display panel on top of which a capacitive sensing panel is provided which includes multiple layers of capacitive sensing circuitry arranged in a pattern.
FIG. 1 illustrates a prior art capacitive sensing panel 100 utilizing a conventional diamond-shaped pattern. The capacitive sensing panel 100 is of a type which is typically provided in a touchscreen panel for an electronic device such as a smart phone, GPS device, tablet computer, mobile media player, remote control device, or any other device capable of using a touchscreen panel. The sensing panel 100 includes an active portion 110 including a sensor pattern configured to assist in the detection of a user touch or hover (for example, through a finger or other body part as well as through a tool such as a stylus). The touchscreen panel 100 is formed from multiple ITO layers, namely, first ITO layer 112 and second ITO layer 114, disposed within the perimeter of the active portion 110. The first and second ITO layers 112 and 114 are separated by a dielectric layer 116. The first ITO layer 112 is patterned to include columns of interconnected capacitive-sensing nodes 113, and a first layer of traces 115A coupled to each column of capacitive-sensing nodes 113 in the first ITO layer 112. The interconnected nodes 113 of any one column are isolated from the interconnected nodes 113 of any adjacent column. The second ITO layer 114 is patterned to include rows of interconnected capacitive-sensing nodes 113, and a second layer of traces 115B coupled to each row of capacitive-sensing nodes 113 in the second ITO layer 114. The interconnected nodes 113 of any one row are isolated from the interconnected nodes 113 of any adjacent row.
In the illustrated implementation, the interconnected nodes 113 have a diamond shape formed by a square rotated by forty-five degrees which allows for an interleaving of the row and column patterns to occupy a large surface area of the active portion 110. Thus, the space between four nodes 113 in two adjacent rows is occupied by one node 113 of a given column. Conversely, the space between four nodes 113 in two adjacent columns is occupied by one node 113 of a given row.
The first and second layers of traces 115A and 115B couple each respective row or column of capacitive-sensing nodes 113 to control circuitry 120. The control circuitry 120 may include drive and sense circuitry coupled to the traces 115A and/or 115B. For example, drive circuitry may be used to apply a signal to a trace 115A for a certain column and sense circuitry may be used to sense a signal on a trace 115B for a certain row. The opposite application of applying and sensing signals may, of course, also be provided using the control circuitry 120.
It is known in the art to operate the sensing panel in at least two distinct modes.
A first mode, referred to herein as a self-capacitance mode, configures the control circuitry 120 to sense the capacitance between any given column or row of interconnected nodes 113 and a surrounding panel reference (for example, ground). By sensing a change in self-capacitance for a given column or row of interconnected nodes 113, the control circuitry 120 may detect a user touch or hover at or near that given column or row of interconnected nodes 113. Advantageously, self-capacitance mode sensing provides the best sensitivity for detecting a user hover. For example, a change in capacitance can be detected with respect to a hover in self-capacitance mode from as far as few centimeters from the surface of the sensing panel 100. Unfortunately, self-capacitance mode sensing is prone to a ghosting problem associated with a multi-touch/hover situation because the entire length of the given column or row of interconnected nodes 113 is used to sense and thus the control circuitry 120 is not able to unambiguously distinguish between different touch/hover instances falling along a same row or column.
A second mode, referred to herein as the mutual-capacitance mode, configures the control circuitry 120 to sense the capacitance at an intersection point between one column of interconnected nodes 113 and one row of interconnected nodes 113. By sensing a change in mutual-capacitance at a given intersection point between a column and row of interconnected nodes 113, the control circuitry 120 may detect a user touch or hover at or near that given intersection point. Advantageously, mutual-capacitance mode sensing provides the best sensitivity for detecting the particular location of a user touch or hover, and enables the control circuitry to distinguish between and identify the locations of multi-touch/hover situations. Unfortunately, mutual-capacitance mode has a weak sensitivity for detecting a user hover. For example, a change in capacitance can be detected with respect to a hover in mutual-capacitance mode from as far as only a few nanometers from the surface of the sensing panel 100.
The opposite advantages and disadvantages of self-capacitance mode and mutual-capacitance mode often lead the system designer to choose operation of the panel in one or the other mode based on whether the panel is being provided in an environment where hover detection (with a lack of accuracy) is preferred or an environment where touch detection (with accurate location) is preferred.
There is a need in the art for solutions which would enable a panel to support both self-capacitance mode and mutual-capacitance mode. For example, those skilled in art could configure the control circuitry 120 to operate in a time division multiplexed configuration which switches the sensing operation back and forth between self-capacitance mode and mutual-capacitance mode. This solution adds complexity to the design of the control circuitry 120 and may further compromise to some degree the sensitivity of the functional operation of each mode. Solutions which would support simultaneous self-capacitance and mutual-capacitance mode operation are preferred.